The present invention generally relates to wireless communication, and particularly relates to tailoring channel quality information messages.
Advanced wireless communication systems such as third generation (3G) systems and beyond employ various techniques for improving data throughput and signal transmission quality. Many of these techniques are based on estimates of instantaneous channel conditions such as path loss and shadowing, interference variations, and fast multipath fading. Instantaneous channel quality conditions are conventionally measured by devices such as cellular phones and are broadly referred to as Channel Quality Indicators (CQIs). CQI values may correspond to Signal-to-Noise Ratio (SNR), Signal-to-Interference+Noise Ratio (SINR), received signal power or strength level, supportable data rates, supportable modulation and/or coding rates, supportable throughput, etc.
CQI information is conventionally transmitted from a wireless receiver such as a cellular phone to a corresponding transmitter such as a base station, e.g., via physical layer signaling. In one example, CQI information is transmitted in Wideband Code-Division Multiple-Access (WCDMA) based system over a dedicated reverse link in compliance with the High-Speed Downlink Packet Access (HSDPA) protocol. Wireless transmission systems use CQI information to assist in radio resource allocation. For example, CQI information may be used to determine transmission scheduling among multiple receivers, select suitable transmission schemes (e.g., the number of transmit antennas to activate), determine bandwidth allocation, select spreading codes, determine modulation and coding rates, etc.
CQI information is conventionally transmitted in the form of a CQI message. Receivers form CQI messages by first measuring channel quality, e.g., SNR or SINR. The receiver then accesses a standardized CQI table where the table contains ranges of uniquely indexed CQI values. The range in which the measured channel quality falls is identified by selecting the corresponding index value. The selected index value is mapped to a sequence of channel quality information bits, e.g., using a (20,5) block coding technique where 5 bits are encoded into a 20 bit-codeword for error protection. The encoded channel quality information bits are then mapped onto a physical channel and transmitted as a message.
The ranges of CQI values stored in a conventional CQI table are fixed and predetermined well in advance of system deployment. In one example, all transmission systems and cells compatible with the 3G Universal Mobile Telecommunications System (UMTS) technology use a fixed table of CQI values having predetermined spacing regardless of individual cell characteristics. In another example, HSDPA also employs a fixed CQI table where the ranges of CQI values are separated by 1 dB power differences regardless of individual cell characteristics. As such, a universal table of CQI values is conventionally used to form CQI message regardless of anomalies or differences that may arise between cells within a radio access network. In addition, both UMTS and HSDPA employ CQI messages having a fixed length of five bits to represent the available ranges of CQI values regardless of individual cell characteristics.